An organic electroluminescent device is a device which spontaneously emits light, and the principle of light emission thereof is as follows. When charges are injected into an organic layer between a hole injection electrode and an electron injection electrode, electrons and holes encounter, combine, and then are annihilated, and thus light is generated. Organic electroluminescent devices have the characteristics of low voltage, high brightness, wide view angle, or the like. Therefore, organic electroluminescent devices have been rapidly developed in recent years. Among these, blue organic electroluminescent devices have become hot spots of investigation due to the wide prospect for application in terms of monochromatic display, white light modulation, or the like.
Trivalent iridium complexes are considered as ideal organic electroluminescent materials in both the academic world and the industrial world all the time, due to the advantages of high luminescence efficiency, adjustable color of light emission, or the like. A number of domestic and foreign research teams have intended to improve the overall properties of the blue organic electroluminescent devices from aspects of material synthesis and device optimization, so as to meet the requirement for industrialization. For Example, an organic electroluminescent device was prepared by a doping method using an iridium complex FIrpic having blue emission as a light-emitting material, by S. R. Forrest et al., at Princeton University, United States, in 2003. Although this device shows an ideal blue emission, unbalanced injection of carriers leads to relatively low efficiency and brightness of the device, and the operating voltage of the device is relatively high.
In order to solve these problems, in 2008, Franky So et al., at Florida University, United States, prepared a blue organic electroluminescent device having a multilayer structure by incorporating an iridium complex having a high efficiency into a preferred host material. This device has relatively high maximal luminescence efficiency, but the current density of the device is relatively low, and the luminescence efficiency rapidly attenuates as the current density increases, resulting in a relatively low brightness and relatively high operating voltage of the device. Furthermore, the complicated structure of the device leads to a relatively high cost of production of the device. Thus, the overall properties, such as luminescence efficiency, brightness, spectral stability, thermal stability, and the like, of the blue organic electroluminescent device are still not effectively improved.